Russ;
Bike frames are built two different ways-- with lugs and without lugs. There
are custom frame fabricators who swear that one or the other is the best--
there is no agreement about which is "best" way to join tubing.
A lugged joint is made by slipping a square-cut end of tubing into a lug
fitting and then nickel-silver brazing the joint with a thin-flowing alloy
such as the Allstate #11 that Howard mentioned. Capillary action wicks the
brazing rod up into the joint and it forms a good, strong shear joint.
A non-lugged joint is fabricated by fillet brazing with Allstate #13 (or
similar). The weld bead looks just like a conventional weld except for its
silvery-gold color. In this type of joint, two tubes are joined directly; no
intermediate "TinkerToy" lug is used.
Which joint is stronger? I've never seen any reliable test data, only strong
opinions and, again, there is no agreement. Fabricators do agree that making
a lugged joint is far easier and cheaper (labor) because the only end
preparation it needs is to be hacksaw cut whereas a non-lugged joint
requires a really tight fit and that ain't easy!
Regards, Neil Tucson, AZ
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